HDF5 tests sometimes hang

[michaelkuhn]

Our HDF5 tests sometimes hang before/in /hdf5/dataset/write_read_selection:

1/1 julea-test RUNNING       
>>> MALLOC_PERTURB_=210 /home/runner/work/julea/julea/bld/julea-test -r /hdf5
▶ 1/1 /hdf5/read_write OK            
▶ 1/1 /hdf5/dataset/create OK            
▶ 1/1 /hdf5/dataset/write OK            
▶ 1/1 /hdf5/dataset/create_delete_open_close EXPECTEDFAIL  
▶ 1/1 /hdf5/dataset/extend EXPECTEDFAIL  
▶ 1/1 /hdf5/dataset/invalid_extend EXPECTEDFAIL  
▶ 1/1 /hdf5/dataset/write_read OK            
Error: The operation was canceled.

I have only seen it on Ubuntu 18.04 and with julea-kv so far.